Re: sizeof PIPE_BUF

> Note that the PIPE_BUF macro is not meant to indicate the size of the
> kernel's pipe buffer.  Check the SUS description of write() for the
> details of what PIPE_BUF means.  The buffer's size must be at least
> PIPE_BUF to satisfy those requirements, but it may be larger.

 Indeed. And as far as I know, there's no strictly user-space way of
knowing the size of the pipe buffer. When I needed to do this, I had
to look deep into the Linux kernel headers, and didn't find anything
either (even the kernel-space PIPE_SIZE macro is defined as PAGE_SIZE
which is 4096). The 65536 value is probably hardcoded somewhere, but
it's obviously not meant to be accessed by a userspace program.

 I guess it's one of the "the specific value is none of your business"
cases, and strictly Single Unix-speaking, it's true; but with the
introduction of the splice() family of system calls, it's still
interesting to know that value. If Felix agrees, maybe he could
suggest it on lkml.

-- 
 Laurent